Synthesis\nof Trisiloxane\nwith the Dioxaborolane Group\nas a Cathode Film-Forming Electrolyte Additive for High-Temperature\nLiMn<sub>2</sub>O<sub>4</sub>/Li<sub>4</sub>Ti<sub>5</sub>O<sub>12<

LiMn<sub>2</sub>O<sub>4</sub> batteries have been widely\napplied\nas various portable electronic devices and electric vehicles owing\nto the merits of low cost, high operating voltage, excellent rate\ncapability, and environmental friendliness. However, the poor performance\nat elevated temperatures remains a serious technical challenge in\nterms of commercial application purposes. A borate-containing trisiloxane\ncompound of TSMBO is designed and synthesized as a cathode film-forming\nelectrolyte additive to improve the electrochemical performances of\nLiMn<sub>2</sub>O<sub>4</sub>/Li<sub>4</sub>Ti<sub>5</sub>O<sub>12</sub> batteries, especially at high temperatures of 55 °C. Atomic\nforce microscopy measurement confirms that the trisiloxane moiety\nin TSMBO can construct a cathode electrolyte interface (CEI) with\nhigher mechanical strength and better flatness compared to the disiloxane\nmoiety in the TSMBO analogue with a similar chemical structure. The\nrobust CEI film on the surface of the LiMn<sub>2</sub>O<sub>4</sub> cathode and the inhibited hydrolysis of LiPF<sub>6</sub> in the\nelectrolyte significantly suppress the dissolution of Mn from the\nLiMn<sub>2</sub>O<sub>4</sub> cathode and maintain the structural\nintegrity of the LiMn<sub>2</sub>O<sub>4</sub> lattice over cycling.\nThus, the LiMn<sub>2</sub>O<sub>4</sub>/Li<sub>4</sub>Ti<sub>5</sub>O<sub>12</sub> coin cell using the TSMBO-containing electrolyte with\nan optimized addition level of 0.5 wt % exhibits a higher capacity\nretention of 49.3% compared with 34.3% for the baseline electrolyte\nafter 300 cycles under 1C rate at 55 °C. The LiMn<sub>2</sub>O<sub>4</sub>/Li<sub>4</sub>Ti<sub>5</sub>O<sub>12</sub> pouch cell\ntests show excellent high-temperature and cycling performance at 55\n°C and a higher capacity retention of 90.4% after 500 cycles\nat 2C compared to 79.7% for that with the baseline electrolyte after\n430 cycles at 2C. This work demonstrates that TSMBO is a promising\nelectrolyte additive for practical use to improve the cycling stability\nof LiMn<sub>2</sub>O<sub>4</sub>/Li<sub>4</sub>Ti<sub>5</sub>O<sub>12</sub> batteries at elevated temperatures.